The Sun Valve


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In 1907 Gustaf Dalén produced perhaps his most famous invention, the sun valve. This turns the beacon on and off using daylight. The first one was erected on Furuholmen’s lighthouse between Stockholm and Vaxholm. The design was so ingenious that many prominent contemporary engineers, including Thomas Alva Edison, doubted that the sun valve could work. The patent office in Berlin went so far as demand a special demonstration before it would approve the patent application.

The sun valve consists of a central, blackened, light absorbing metal rod surrounded by three gilt light-reflecting metal rods, all parallel with each other. In darkness all the rods are the same temperature and length. When dawn breaks the blackened rod absorbs light energy and acquires a slightly higher temperature than the shiny rods. The blackened rod becomes very slightly longer than the shiny ones triggering a device which cuts off the gas and switches off the lighthouse light.
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When dusk falls, the blackened rod contracts, the gas valve opens and a small pilot flame lights the beacon. Combined with the flashing apparatus, the sun valve saves 94% of the gas compared with having the beacon alight all the time.